Study: Sharing ratios, RSS good for Bittorrent

There have been lots of debates in the Bittorrent community about the subject of sharing ratios. Some Bittorrent websites are tracking their members' sharing behavior across multiple torrents to force people to contribute. Users with a low upload to download ratio might get punished by having their accounts revoked or being barred access to new content.

Bittorrent inventor Bram Cohen came out strongly against sharing ratios a few weeks ago. Cohen claims that the Bittorrent protocol can deal with people contributing less than the amount of data they download. He blaimed sites with enforced sharing ratios for people trying to cheat those ratios in an interview with Zeropaid.com:

"Sites which do this are being extremely destructive, and the way they grandstand about how they're fostering sharing really ticks me off."

Matei Ripeanu, Miranda Mowbray, Nazareno Andrade and Aliandro Lima seem to disagree. The four scientists just published an extensive paper about Bittorrent at First Monday. They analyzed the sharing behaviour within six Bittorrent communities - and came to the conclusion that sharing rations and other social norms can be beneficial to a community:
"Easytree’s sharing ratio enforcement mechanism has, in some cases, the side effect of creating a motivation to upload original content, a type of contribution that requires more effort than simply uploading existing content. A member whose sharing ratio is below the low sharing threshold cannot join new torrents. In this situation, one way for the member to raise its sharing ratio is to contribute new content. In this case there is a substantial reward for the extra effort: regaining the ability to join new torrents."

However, sharing rations are not the only way to ecourage users to contribute. Some other methods are more technical and less obvious:

"For example, a user may subscribe to an RSS feed of a site that publishes past episodes of television series, and state interest in any new episode from a particular series. Whenever the RSS feed announces matching content, the user’s client will download it automatically. In the time between finishing a download and the user checking to see whether new files have arrived, the client remains connected as a seeder. Thus, as a side effect, broadcatching results in increased seeding and sharing because users maintain their clients running for longer time."

Some of the data used for the study seems to be a little older - they analyzed Btefnet, a site that is offline since it got sued in May 2005 by the MPAA - but it's still a fascinating read for anybody interested in the inner workings of Bittorrent and P2P sharing / gifting economies.

You're right, there is no definite correlation between RSS feeds and increased seeding ... but it is interesting as a possible explanation.

It certainly makes sense that seeding might increase when it is not only a conscious deicision by the seeder, but something that happens automatically in the background.

And yes, towards some degree that is already true for regular Bittorrent downloads - but when someone is starting a download himself he might be more inclided to finish it at a given time as well than when his computer takes care of such things.

And regarding the enforcement of share ratios: The authors shy away from endorsing it, but recommend the use of social norms - one of which is the tracking of rations across multiple torrents. Maybe you don't even have to ban people if you can shame them into sharing ...

Hello, I'm one of the authors of the paper.
Ernesto99 says:
> The authors don't list enforcing sharing ratios in the suggestions
> to increase contribution levels.
That's because our list of suggestions is for gifting technologies in general, not for BitTorrent in particular. The administrators of one site told us that when they introduced sharing ratio enforcement, contribution levels went up - this is just anecdotal evidence, of course, but it fits with the results that we found.

> it is strange to attribute the seeding
> percentates to the rss feeds while there
> are hundreds of other differences between
> the sites that can explain the variation.
I agree that our data is not conclusive, although we did control for some other differences (torrent age distribution, file size distribution, combinations of the two) using partial regressions.

However, any other explanation has to account for both the high seeding in the site that used rss feeds, and also the fact that the distribution of this seeding between different torrents was more even in the site that used rss feeds than in any of the other sites we looked at. The even distribution to me suggests that the increased seeding is the result of some structural or mechanical factor, rather than human variation. I can't think of a structural/mechanical factor other than the rss feeds that btefnet had and the other sites don't have and that would be likely to increase seeding. If you can think of one, I'd be interested.

Hello Janko,
> At what time did you gather the data?
As you guessed, most of the data is quite old (on Internet timescales); the btefnet data was gathered in March 2005. The alluvion data is the most recent, from August 2006.